Studies on the dynamic syn-anti equilibrium in purine nucleosides and nucleotides with the aid of 1H and 13C NMR spectroscopy.

Analyses of 1H and 13C NMR spectra have been utilized to extend studies on the dynamic equilibrium syn-anti about the glycosidic bond of purine nucleosides and nucleotides. With the aid of chemically synthesized model analogous in fixed syn and anti conformations, and the introduction of appropriate corrections for the conformation of the exocyclic chain of the sugar moiety, it is possible to evaluate quantitatively the relative populations of the syn and anti conformers from the experimentally observed chemical shifts of H(2') and C(2'). The resulting agreement between the data based on H(2') chemical shifts with those deduced from C(2') chemical shifts extends the validity of this procedure, and furnishes more accurate results than those previously based on uncorrected H(2') chemical shifts alone. The overall findings are briefly compared with those derived from measurements of proton relaxation times and the Overhauser effect, as well as by X-ray diffraction in the solid state. Attention is drawn to the potential utility of the results, including chemical shift data, in studies on interactions of nucleosides and nucleotides with appropriate enzyme systems.